Cathode for electric discharge devices



May 14, 1935.

E. RMHILD CATHODE FOR ELECTRIC DISCHARQE DEVICES Filed Jah. l5, 1952 HisAttorney.

Patented May 14, 1935 UNITED STATES CATHODE FOR ELECTRIC DISCHARGE vDEVICES Edgar Rmhild, Berlin-Steglitz, Germany, assignor to GeneralElectric Company, a corporation of New York Application January 15,1932, Serial No. 586,933 In Germany January 22, 1931 6 Claims.

The present invention relates to cathodes for electric discharge devicesand more particularly to cathodes designed to carry large current atrelatively low voltage.`

5 Heavy current cathodes of large power tubes are sometimes constitutedof metal strips having a serpentine, loop or spiral conguration andpresented edgewise to the anode. These shapes are desirable in vorder toobtain large cathode sur- 10 faces in relatively small spaces and tominimize radiation of heat. When cathodes of this sort are heated, thefolds or convolutions, upon expansion, tend to distort and to changetheir relative position with respect to one another and also withrespect to the cooperating electrode, thus causing deleteriouskoperating effects. Furthermore, these cathodes are subject tomechanical distortion by rough handling.

An object of the present invention is to provide an improved arrangementfor holding a cathode structure of the type referred to rigidly in shapeunder unheated conditions, i. e., during manufacture; also under heatedconditions as when being operated. This object is attained in brief, byforming the strip into a series of recurring reverse loops of which theinner portions are held rigidly between two grooved insulating disks.The latter may be supported on a central rod to which they are rigidlysecured.

The invention will be better understood when reference is made to thefollowing description and accompanying drawing in which Fig. 1 is across-sectional view of a cathode bent to form and shown as being ttedinto one of the insulating disks or plates; Fig. 2 is a cross sectiontaken along line 2 2 in Fig. l; Fig. 3 shows the disposition of theimproved cathode with respect to an anode of an electron dischargedevice; Fig. 4 is a diagrammatic view of an improved cathode providedwith a control member and a cooperating anode; Fig. 5 shows plan andeleva- .tional views of the insulating plate.

Referring to Fig. 1, numeral l designates a strip form of cathodeconstituted of a member of bent and straight portions which take thegeneral design of a clover leaf. The cathode may be fabricated of anysuitable metal, for example, nickel, and if desired, coated withelectronically active material. As shown more clearly in Figs. 2 and 5,the inner portions of the cathode are held rigidly between two circularplate members or disks 2 constituted of insulating material. Thesemembers are held at the proper distance apart by a spacer member 3 ofinsulating material and the entire assemblage arranged on a metal rod 4to which it is rigidly secured by a washer 5 and pins 6 driven throughthe rod. The plates 2 are provided with channels or grooves l whichreceive snugly the inner loops.

As shown in Fig. l, one of the inwardly projecting loops of the cathodemay be broken to provide terminals 8 for the application of alter'nating or direct current. If desired, the loops mays be entirelyunbroken so as to form a continuous annulus and provided withconnections at symmetrically disposed points on the cathode tok which amulti-phase voltage may be applied. It is evident that regardless of themanner in which current is passed through the` cathode, the structuralarrangement, including the supporting disks 2, the spacer 3 and thecentral rod is such as to preclude any movement of the cathode as aWhole, or the individual portions thereof in any direction. As thecathode is heated, the resulting expansion is taken up by thelengthening of the individual convolutions, which simply results in aslightly increased outer diameter of the cathode and does not producedistortion of the individual loops because the metal is free to movelongitudinally through the grooves. It is also apparent that a cathodeof the type shown, when presented edgewise to an anode is capable ofproducing a large electron current 'by reason of its active surface andconfiguration which tends to prevent undue heat radiation; also onaccount of the f large extent of the surface. A cathode of this type isrelatively easy to manufacture and assemble.

In Fig. 3, I have indicated the spacial relation of the improved cathodewith respect to an anode of an electron discharge device. Numeral 9design nates an anode of symmetrical shape such as a frustum of a cone,and presented endwise to the cathode. In order to prevent the anode frombeing coated with active material sputtered from the cathode, the lattermay be provided with a metal shield Il) in the form of a shallow dishwith the concave surface presented to the cathode. The shield member maybe provided with a raised portion l I secured to the central rod Il inany suitable manner, for example, by a pin I2 driven through the rod.

The improved form of cathode lends itself to electron discharge devicesof the electrostatically controlled type. Thus, in Fig. ll, I show ametal cylinder I3 surrounding a loop cathode of the improved type andclosed at both ends except for perforated portions for the escape ofelectrons. The cylindrical member terminates in a metal tube I4 whichmay be sealed to the glass envelope of an electron discharge device.'I'he central rod member 4 may also be secured to a stem. The upper endportion of the electrostatic control member is provided with a angeextension l5 which carries a pin I 6 driven through the central rod. Thestructure as a Whole, i. e., the improved cathode and grid member, isthus arranged in a compact and rigid unit which precludes relativemovement between the cathode and grid so that small spaces may beaccurately maintained between the electrodes. A combined cathode andgrid structure of this sort may be employed in connection with asymmetrical form of anode 9 to which it is presented endwise.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A cathode for an electron discharge device comprising a metallicstrip member bent into recurrent inner and outer loops and arrangedabout a central support member, means for securing the inner loops tothe support member, said means comprising a pair of insulating platescontaining grooves which receive the loops.

2. A cathode for an electron discharge device comprising a metallicstrip bent into recurrent inner and outer loops and arranged about a.central support member, means for securing the inner loops to thesupport member, said means comprising a pair of insulating plates spacedapart by an insulating member, said plates serving to clamp the stripbetween them.

3. A cathode for an electron discharge device comprising a metallicstrip having recurrent loops which form in the aggregate, roughly acylinder, a support member mounted in the axis of the cylinder, andextending over and secured to the edges of said loops.

4. A cathode for an electron discharge device comprising a metallicstrip having recurrent loops which form in the aggregate, roughly acylinder, a support member mounted in the axis of the cylinder andsecured at both ends to said loops.

5. A cathode for an electron discharge device comprising a metallicstrip bent into recurrent loops and forming a complete annulus, saidannulus being provided with terminals, greater in number than two,equidistantly spacedabout the periphery of the annulus for theapplication of multi-phase alternating current to the cathode.

6. An electron discharge device including a cathode, an electrostaticcontrol member and an anode, said cathode and electrostatic controlmember secured together as a unit, said cathode being constituted ofstrip material presented edgewise to said anode and having recurrentloops arranged about and supported from a central member, said controlmember being constituted of a perforated cylinder secured to saidcentral support member.

EDGAR ROMHILD.

